Air Filter Cleaning – Replacement Guide for 1987 Yamaha YZ125

Shop parts for a 1987 Yamaha YZ125 Dirt Bike.

The air filter on a 1987 Yamaha YZ125 is essential for protecting the engine from harmful dirt and debris while ensuring optimal airflow for peak two-stroke performance. Keeping the filter clean – or replacing it when needed – is especially crucial on this classic motocross bike, as dust and ingress can quickly damage the YZ125's high-revving engine. Follow these MotoSport-exclusive steps to maintain your air filter and keep your YZ125 running strong and reliable.

Tools & Supplies Needed

  • Rubber or disposable gloves
  • 10mm socket wrench
  • Air filter cleaner and oil (petroleum-based or biodegradable type)**
  • Soft, clean bucket for washing
  • Soft brush or rag (if needed, avoid aggressive scrubbing)
  • Clean, dry towels
  • Rim grease or sealing grease

**Always check your specific filter oil instructions, especially if using a biodegradable product – cleaning requirements may vary.

How to Remove the Air Filter

  1. Remove both side panels and the seat using a 10mm socket. Set all fasteners in a container so you do not lose them.
  2. Carefully unscrew the wing nut holding the air filter cage in place.
  3. Gently pull the filter and cage out as one unit.
  4. Important: Cover the exposed air intake with a clean cloth or rag immediately to prevent dirt from entering the engine.

Cleaning the Filter

  1. Take the filter off the cage; check the cage for cracks or damage.
  2. Tap the filter to remove any loose debris.
  3. Soak the filter in a bucket with appropriate filter cleaner. Let it sit for a few minutes.
  4. Gently squeeze (do not wring or twist) the filter to push out contaminants. Repeat soaking and squeezing until the filter appears clean and water runs clear.
  5. Rinse thoroughly with clean water, again squeezing out (not wringing) excess moisture.
  6. Let the filter dry entirely. Air drying is best; avoid using high heat which can damage the foam.

Oiling and Reinstalling the Filter

  1. Once dry, evenly apply air filter oil throughout the foam. Massage oil to ensure complete saturation but avoid over-oiling, which can restrict airflow.
  2. Apply a thin layer of rim grease/sealing grease to the sealing edge to keep dust out of the intake.
  3. Reinstall the filter on its cage and verify alignment.
  4. Remove rag from the airbox, then fit the air filter/cage assembly back in place. Secure with the wing nut.
  5. Reinstall seat and side panels, making sure all fasteners are tight and the seat is properly aligned with the frame groove.

Replacement Tips & When to Consider a New Filter

  • If the filter foam is brittle, torn, or does not return to shape after squeezing, replace it immediately.
  • Dirty or over-oiled filters mean increased risk of clogging and engine damage.
  • Plan on cleaning the filter after every very dusty ride or every couple rides for regular track use; more often in sand or mud conditions.

Key Notes for 1987 Yamaha YZ125 Owners

  • The 1987 YZ125 uses a unique twin-air filter cage design compared to later models. This means ensuring the cage's integrity and a tight seal is especially critical on this year.
  • Due to the YZ125's rev-happy two-stroke engine, a clean, well-oiled filter is particularly crucial for maintaining throttle response and preventing expensive internal wear.
  • This model's airbox can be more prone to water intrusion. After each filter clean, inspect the airboot and inside airbox for moisture or signs of dirt ingress – wipe clean as needed.

With regular filter service, your 1987 Yamaha YZ125 will breathe clearly and run at full potential – keeping you ahead of the pack and maximizing the iconic power of this classic motocross machine.

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Disclaimer: This guide is provided for general informational purposes only and is not intended to replace your motorcycle's official owner's manual. Always refer to your manufacturer's documentation for model-specific instructions, torque specifications, safety procedures, and maintenance requirements. If you are unsure or inexperienced, consider seeking assistance from a qualified mechanic or technician.